1. Field of the Invention
The present invention relates generally to radio communications, and particularly to a communications radio for use with multiple narrowband and wideband signal waveforms.
2. Discussion of the Known Art
Radio frequency (RF) transmitters and receivers for the Joint Tactical Radio System (JTRS) typically have bandpass filters arranged in intermediate frequency (IF) stages of the communications equipment to support the reception and transmission of signal waveforms defined by the JTRS. The waveforms are referred to as being either “narrowband” or “wideband” depending on the bandwidth needed to pass them through various stages of the equipment without distortion. Waveforms whose bandwidths are less than 3 MHz wide are generally considered narrowband, and waveforms with bandwidths of 3 MHz or greater are referred to as wideband. Typical uses and bandwidth requirements for several JTRS signal waveforms including WNW, SRW, NCW, HNW, and MUOS are disclosed in T. Mann, JTRS/WIN-T: Networking Waveform Quick Reference Sheets, on the Web at findarticles.com/p/articles/ (Summer 2008), which is incorporated by reference. See also, IT Mentor Group, Inc., Joint Tactical Radio System, on the Web at itmentor.com/jtrs.htm; and Joint Tactical Radio System, at en.wikipedia.org/wiki/JTRS.
Under the JTRS, one GMR communications platform may operate on up to four frequency channels, wherein each channel carries one of the JTRS waveforms (e.g., EPLRS, SINCGARS, HF ISB/SSB/ALE, SRW, WNW, or UHF DAMA SATCOM). See, P. H. Sniffen, Joint Tactical Radio System: AMF, GMR, HMS, on the Web at low-powerwireless.com/blog/designarticles/ (March 2012), which is incorporated by reference.
U.S. Pat. Pub. 2006/0114969 (Jun. 1, 2006) describes a data transmission device including an array of four surface acoustic wave (SAW) filters the inputs of which are switched selectively to receive a pulse signal, and the outputs of which are combined to produce analog signals having different frequency characteristics. U.S. Pat. No. 7,460,851 (Dec. 2, 2008) discloses a device for integrating a single SAW filter and a transceiver by encapsulating them to form an integrated chip. Neither patent document suggests a filter array that supports multiple narrowband and wideband waveform operation in radio equipment, however.
Small form factors specified by the military for tactical vehicular radios, as well as cost considerations, tend to limit the number of filters that can be provided with associated switches and discrete matching elements (resistors, inductors, and capacitors) inside one radio. For example, as shown in FIG. 1, an IF signal stage of a radio developed by BAE Systems includes a switched bank or array 10 of two SAW bandpass filters 12, 14, for enabling the bandwidth of the stage to be set to either 0.5 MHz or 1.2 MHz. The filters 12, 14, switches 16, 18, and discrete elements for matching the filters electrically with the IF stage, are arrayed individually over an area of defined length and width on the surface of a circuit board 20. The dimensions of the radio are within the form factors specified by the JTRS for Ground Mobile Radio (GMR), but it supports only a small subset of the various JTRS waveforms. Therefore, there is a need for a compact filter array or package that allows a radio to operate with multiple narrowband and wideband signal waveforms, without exceeding the physical dimensions of present narrowband waveform filter arrays.